If I had to figure out which plant was the space alien, I’d peg the poison ivy. Like Star Trek’s Borg, it seems to be saying Resistance is futile. It accounts for three quarters of the vegetation along some nearby streets. It shoots up tree trunks, with bright aerial roots that seem to be assimilating the trees.
It withstands herbicides, drawing on its extensive root system to rally, sometimes
returning the next season, gnarled but unrepentant.

A low plant, a bush, a vine on the ground, or a vine that climbs trees.

Flowers

Showy white or cream clusters, each flower about 1" (2.5 cm) across, with five petals and many stamens.

Small, yellowish-green, inconspicuous.

Leaves

In clusters of three; clusters are opposite to each other, not alternating.

In groups of tree, shiny when young, alternating.

Seeds

Soft, silky fluffs.

Fruit

Small greenish-white berries.

Range/ Zones

USDA Zones: 3-8

Habitats

Low, moist woods; thickets; stream banks

Disturbed areas, roadsides, waste areas

Type

Wild

Wild

Occurrence

Common

Common

Identification: Young poison ivy has furled red shiny leaves. The leaves unfold, becoming dark green, remaining shiny, 1-2" (2.5-5 cm) long. Leaves are in groups of 3. (Leaves of three, let it be.) As the plant ages, the leaf color lightens and the characteristic shine lessens and disappears. Notice the spikes that are present on most leaves. If you see a vine climbing a tree, and it has myriad rootlets reaching into the bark, it is probably poison ivy. It may also appear as a bush or a vine creeping along the ground. In the fall,
leaves are bright red. Flowers are small and yellowish-green, and berries are dull white or greenish-white. Poison ivy has two relatives, poison oak and poison sumac. Poison oak looks a little similar.

Edibility: Poisonous Every part of poison ivy, leaves, berries,
and roots, contains urushiol, the stuff that triggers an immune reaction—a blistering rash that persists for 2-3 weeks.
Even the leaves from last fall are dangerous. Fumes from burning poison ivy create extremely painful blisters inside your lungs, and can be life-threatening. What can you do if you’ve been exposed? By many accounts, spotted jewelweed will reduce the symptoms. This common plant is often found near poison ivy. Crush the stems and rub the juices over the exposed areas. If possible, doff your clothes so that any resin on them won’t cause further problems, and shower. The shower won’t help areas that are already exposed, but it will reduce the chance of spreading. If you think you’ve breathed burning poison ivy, or get it in your eyes, or have an exceptionally severe reaction, see a doctor. More information is available here and in the spotted jewelweed article.

Think you’re immune to poison ivy? Most of us are, the first one or two times we are exposed. But sensitivity increases with repeated exposures. At least 80% of people are allergic. Later in life, sensitivity begins to wane again.

A study completed in 2006 (see article) examined the effects of rising levels of carbon dioxide (CO₂) on plant growth. Since plants breathe CO₂ and release oxygen, one might expect that rising CO₂ would aid in plant growth. In fact, though, most plants are relatively unaffected by excess CO₂. But in a simulation of the CO₂ levels that will exist by 2050—50% higher than they are now—poison ivy grew at three times its normal rate. Urushiol, the stuff that causes a rash, occurs in saturated and unsaturated forms. In the high CO₂ poison ivy, the unsaturated form accounted for 20% of the urushiol, vs. 15% in today’s plants. The unsaturated form is much more poisonous, so this “super-ivy” will be more of a threat.